Isospora belli; Cystoisospora belli

Epidemiology

• oocysts are passed in feces which mature to infectious sporozoites in the environment
  • oocysts in the environment may remain infectious for months
• human to human fecal-oral transmission
• no animal reservoir identified
• infection most common in South America, Africa, and Southeast Asia

Pathology

• undergoes both sexual & asexual reproduction in the cytoplasm of epithelial cells in the small intestine
• sexual reproduction results in production of oocysts which a passed in feces

Clinical manifestations

• watery diarrhea (non-bloody)
• abdominal pain, cramps
• malabsorption, anorexia, malaise, vomiting, fever
• generally self-limited, except in patients with AIDS or other immunodeficiency syndromes

Laboratory

• Isospora belli in stool
• diagnosis is made by finding unsporulated oocysts in feces
  • measure 12 by 30 microns
  • infectious oocyst contains 2 sporocysts, each with 4 sporozoites
  • direct wet mount or concentration methods
  • oocysts stain with acid-fast stains
  • ultraviolet autofluorescence microscopy
• sporulation occurs if feces specimen is left unfixed for 24-48 hours
• Isospora belli DNA

* images

Management

• supportive therapy, fluid & electrolyte replacement
• Bactrim DS (160/800)
  • 1 PO QID for 10 days, then
  • 1 PO BID for 21 days
• ciprofloxacin is alternative
• pyrimethamine 50-75 mg/day
• maintenance doses may be required to prevent relapses with HIV1 infection
  • Bactrim DS, 1 PO 3 times/week
  • sulfadoxine 500 mg plus pyrimethamine 25 mg weekly

More general terms

• Isospora

Additional terms

• isosporiasis
• oocyst
• sporozoite